A technique to improve an exhaust performance of an internal combustion engine and to improve a fuel consumption of the internal combustion engine by introducing exhaust gas to an intake system in accordance with an driving state, viz., by performing, so-called, an EGR is conventionally known.
In addition, a structure such that, when the EGR is performed, a part of exhaust gas is re-circulated toward an upstream side of a compressor of a turbocharger disposed in an intake passage is conventionally known.
For example, a Patent Document 1 describes such a technique that, when a driving state is switched to a state in which an EGR gas quantity introduced from an upstream side of a compressor of the turbocharger disposed in an intake passage is increased more than the present time, an internal EGR is increased by modifying a valve timing by means of a variable valve timing mechanism and an insufficient quantity of an external EGR is compensated by the internal EGR at a transient time of the switching.
However, this Patent Document 1 does not specifically disclose at which timing a valve timing to increase the internal EGR is ended, when the variable valve timing mechanism is used to increase the internal EGR. Therefore, for example, when the valve timing such that the internal EGR compensates for the insufficient quantity of the external EGR rate within a cylinder is ended after the EGR rate within the cylinder has reached to the target value, there is a possibility that the EGR rate within the cylinder overshoots or undershoots with respect to the target value of the EGR rate within the cylinder due to an operation delay of the variably valve operated mechanism.